ST9 datasheet(125/146 Pages) STMICROELECTRONICS

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ST9 USER GUIDE

Once you have set these registers, the core is in good shape to start work. The next task is to

initialise the data memory and/or register file by entering a loop that writes zeroes into all lo-

cations used for data storage. This may seem superfluous, but there are two reasons for this:

– In C language, any non-initialized variable is supposed to contain zero at as an initial value.

– In any case, this makes the program behavior reproducible, even if not all variables are ini-

tialized explicitly.

Then, the table of initial values for the initialized variable (in the C language sense) is copied

to the location in RAM where the variables are positioned. The linker puts the initial values in

the same order as the variables in RAM, so a mere block copy is sufficient for this initialisation.

Eventually, the entry point of the main program written in C or assembler can be called. The

main program should be a closed loop and should not return. Typically in the start-up code,

the call to the main routine is followed by a halt instruction.

5.4.3.3 Start-up File Customization

A generic start-up file is included with the Toolchain: crtbegin.spp. This file has to be modified

in order to fit the needs of your application.

In most cases, only two parts should be modified: part 2 (interrupt vectors declaration) and

part 6 (MMU setup).

Note:

The start-up file initializes the “ST9” mode (ENCSR bit of EMR2 to 0) to be compatible with the

previous ST9 version. In the main program you have to initialise this bit to 1 for “ST9” mode if

you want the MMU working with segments during interrupts.

ST9 Datasheet(PDF) 125 Page - STMicroelectronics